Dissimilar welding of aluminum (Al) alloy to steel has been a long-running scientific and technological problem mainly for the automotive industry. It would allow to achieve new designs of optimized vehicle structures combining strength, lightweight and energy absorption ability. However, the weld strength is limited because of a brittle intermetallic layer (IML) formed at the weld interface. In our previous study, we demonstrated a significant improvement in weld strength by the addition of Ni to Al alloy. However, the effect of Ni addition on the fracture properties of IML remains unexplored. Moreover, additional Ni should also affect the yield strength and deformability of Al alloy itself. Hence, in this study, a hybrid inverse modeling technique was used to determine the fracture properties of IML. Digital image correlation (DIC) was used to measure the displacement field across the sample surface during tensile shear tests. Finite element model (FEM) with a cohesive zone model (CZM) was used to model the fracture through the IML between Al and steel. Displacement filed experimentally measured by DIC was applied to the FEM to precisely identify the CZM parameters, i.e. interfacial strength and fracture energy of IML. This hybrid DIC-FEM inverse modeling technique was used to analyze different Al/steel welds with varying composition of Al alloys (AA1050 and Al–Ni). From a wide range of tentative interfacial strength and fracture energy for the CZM, this study clarified that the interfacial strength of IML formed et al.–Ni/steel weld was higher than that of AA1050/steel weld.